Ko Sarai (Thai: เกาะสาหร่าย, pronounced [kɔ̀ʔ sǎːràːj]) is a subdistrict (tambon) in Mueang Satun District, Satun Province, Thailand. It is composed of 3 island groups, totaling 243 km2, and has a population of 5077 as of 2012[citation needed] .